1. Field of the Invention
The present invention relates generally to stents for use in supporting and maintaining an open lumen within a body passage or vessel and, more particularly, to stents configurable between large and small diameters.
2. Description of Related Art
Tubular prosthesis, which are commonly referred to as stents, are used to reinforce or strengthen body passages or vessels. Occluded, collapsed, or compromised body passages, such as blood vessels, esophagus, tracheas, gastrointestinal tracts, bile ducts, ureters, and urethras, can all benefit from stents. These body passages can become occluded, collapsed, or compromised from disease, trauma, or from specific surgical procedures upon the wall of the body passage.
Prior art stents typically comprise a length of plastic tubular material, having a number of side holes disposed along the length of the plastic tubular material. U.S. Pat. Nos. 4,913,683; 4,643,716; 5,282,784; 4,957,479; 4,931,037; and 5,364,340 describe stents generally constructed in this manner. Each of these stents has a generally fixed diameter and, therefore, is non-responsive to the specific diameter of a vessel.
A prosthesis or stent capable of expanding to appropriate diameters, along the length of the stent, can provide advantages over fixed-diameter stents. Self-expanding stents are disclosed in U.S. Pat. Nos. 5,026,377 and 5,078,720, both issued to Burton et al.; U.S. Pat. No. 5,019,085 issued to Hillstead; U.S. Pat. No. 4,969,458 issued to Wicktor; and U.S. Pat. No. 5,041,126 issued to Gianturco. These self-expanding stents are typically held in a contracted condition during insertion into the body passage or vessel and, after being positioned within the passage or vessel, released to expand fully. The stents of Wicktor and Gianturco comprise coiled or looped wires, which are unable to contact the entire surface of the interior wall of the affected vessel. The Hillstead stent incorporates a multiple-loop wire structure, which suffers from the same deficiencies associated with the Wicktor and Gianturco stents. U.S. Pat. No. 5,507,767, issued to Maeda et al., discloses a self-expanding stent that employs a plurality of straight stainless steel wire sections, separating a plurality of bends, that may be adjusted and set to fit a particular anatomy or condition. U.S. Pat. No. 5,476,505 issued to Limon discloses a coiled stent for introduction into a body passage at a first diameter and subsequent expansion within the body passage to a second diameter. This coiled stent relies on a procedure for holding a coil in a tightly-wound condition during insertion of the coiled stent. U.S. Pat. No. 5,409,019 issued to Wilk discloses a stent, which surrounds a balloon, so that the collapsed balloon, upon expansion, can expand the stent. U.S. Pat. Nos. 5,078,720 and 5,026,377 issued to Burton et al. describe a combination of a self-expanding braided stent and an instrument for deployment or retraction of the stent. The instrument for deployment or retraction of the stent includes a tubular sleeve, which surrounds and compresses the braided stent. This surrounding tubular structure requires that an additional wall thickness, corresponding to a thickness of the tubular sleeve, be added to the device during placement. Consequently, a shortcoming of the Burton et al. invention is that the placement of the device is the time when the lowest profile or smallest diameter is required.
A need remains in the prior art for a prosthesis or stent which can be placed accurately into a low-profile or small-diameter condition and which can expand in diameter to a predictable size with a predictable pressure applied to an interior surface of the vessel wall. A need also exists in the prior art for a stent having a retention feature for maintaining the stent in a preferred position within the body passage. Additionally, a need exists in the prior art for a stent having a diameter, which is capable of responding and changing to the development of the lumen of the vessel or passage.
The stent of the present invention can be introduced into a body passage or vessel in a low-profile or small-diameter and, subsequently, expanded to a large diameter. The stent can be inserted into the body passage over a guidewire or small gauge catheter in the small diameter configuration. After the guidewire or small gauge catheter is removed, the stent is transformed into the large diameter configuration, Which stimulates the reactive nature of the body passage to thereby develop or maintain a patent lumen. The stent is able to provide maximum communication and flow of fluids from the surface of the stent to the other surface of the stent.
The stent of the present invention is formed of an elongate, flexible duct having a very thin wall and a preformed diameter, length, and shape. The stent is constructed of a woven tubular structure of multiple strands of elements. The woven tubular structure is thermally set to a predetermnined diameter and length, so that the xe2x80x9cat restxe2x80x9d or natural condition of the tubular structure is predictable. A retention or holding member can be formed at one or both of the ends of the stent. This retention member can be reduced in diameter or deformed or straightened for insertion into the body passage. The woven tubular structure provide a path for fluids to flow in and around the stent, while a patent lumen is being developed. The woven tubular structure allows the stent to be extended or stretched over a guidewire or other non-compressive member, to thereby reduce the diameter of the stent for insertion of the stent into a body passage.
The woven or braided stent can be formed from elements, such as polymers including polyester and metals such as Nitinol and titanium. These elements have a high-tensile strength and thereby resisting any breakage of the stent. Notwithstanding this high strength and structural integrity, the elements are generally movable relative to each other thereby providing the stent with an overall desirable, soft characteristic.
Various materials can be used to form the individual elements of the weave or braid. These materials can provide each element and the stent as a whole with considerably different characteristics at the operative site. The elements can be provided with absorbent characteristics facilitating a controlled release of drugs, chemicals, and other absorbents having medical characteristics.
In one aspect of the invention, a method of iteratively increasing a diameter of a lumen of a body passages includes the steps of inserting and moving a stent through the body passage to a desired location. At the operative site, the diameter of the stent is iteratively increased in a first iteration which provides the lumen with a first enlarged diameter and a second iteration which provides the lumen with a second enlarged diameter.
In another aspect of the invention, the stent is formed with a plurality of filaments disposed along an axis of the stent and providing the stent with an outer surface which is generally cylindrical in configuration. A material is disposed relative to the filaments which maintains the filaments in a predetermined orientation at least during insertion of the stent into a body conduit. This material may initially provide the filaments with generally rigid properties in the presence of the material and generally flexible characteristics when the material is removed.
In a further aspect of the invention, a stent is provided with a body having first characteristics advantageous during insertion of the stent and second characteristics advantageous when the stent is operatively disposed in a body conduit. A material disposed relative to the body has first properties facilitating the first characteristics of the stent body during insertion and second properties facilitating the second characteristics of the stent body when operatively disposed. The material may be bio-absorbable, and impregnated into or coated on filaments forming the body.
In still a further aspect of the invention, the stent may include a first element with first a first absorbent providing the stent with properties dependent upon the medical characteristics of the first absorbent. A second element can be included in the stent and provided a second absorbent having absorption characteristics which differ from those of the first element.
The present invention, together with additional features and advantages thereof, may best be understood by reference to the following description taken in connection with the accompanying illustrative drawings.